Novel circularly polarized antennas with a circular radiating aperture for broadband characteristics are presented in this paper. The vertical and horizontal components of the L-shaped probe are separated and placed at the front and back side of the substrate. The antennas are excited by a microstrip line which is connected to the vertical component of the L-shaped probe and electromagnetically couples the signal to the horizontal component of the L-shaped probe. A novel concept of placing stub in the slot of a planar antenna, by observing the electric field vector behaviour in the slot, is proposed to enhance the axial ratio (AR) bandwidth by around 10%. Unidirectional patterns can be obtained by having a cylindrical cavity of height λg/4 behind the antenna and is effective when no stubs are placed in the slot. A < 3 dB AR bandwidth of 39.5% with cavity and 41.18% without cavity but with stub in the slot is obtained in simulation and the results well match with the measurement.
2. Fukusako, T., K. Okuhata, K. Yanagawa, and N. Mita, "Generation of circular polarization using rectangular waveguide with L-type probe," IEICE Trans. Commun., Vol. e86-B, 7, Jul. 2003.
3. Yang, S. S., K. F. Lee, A. A. Kishk, and K. M. Luk, "Design and study of wideband single feed circularly polarized microstrip antennas," Progress In Electromagnetics Research, Vol. 80, 45-61, 2008.
4. Masa-Campos, J. L. and F. Gonzalez-Fernandez, "Dual linear/circular polarized planar antenna with low profile double layer polarizer of 45°tilted metallic strips for WiMAX applications," Progress In Electromagnetics Research, Vol. 98, 221-231, 2009.
5. Tseng, L. Y. and T. Y. Han, "Microstrip fed circular slot antenna for circular polarization," Microw. Opt. Technol. Lett., Vol. 50, No. 4, 1056-1058, Apr. 2008.
6. Chen, H. D., "Broadband CPW fed square slot antennas with wideband tuning stub," IEEE Trans. on Antennas Propag., Vol. 51, No. 8, 1982-1986, Aug. 2003.
7. Jiao, J. J., G. Zhao, F. S. Zhang, H.-W. Yuan, and Y. C. Jiao, "A broadband CPW-fed T-shape slot antenna," Progress In Electromagnetics Research, Vol. 76, 237-242, 2007.
8. Preradovic, S., I. Balbin, N. C. Karmakar, and G. Swiegers, "A novel chipless RFID system based on planar multiresonators for barcode replacement," 2008 IEEE International Conference on RFID, 289-296, Apr. 2008.
9. Qu, S. W., C. H. Chan, and Q. Xue, "Ultrawideband composite cavity backed folded sectoral bowtie antenna with stable pattern and high gain," IEEE Trans. Antennas Propag., Vol. 57, No. 8, 2478-2483, Aug. 2009.
10. Shi, S., K. Hirasawa, and Z. N. Chen, "Circularly polarized rectangularly bent slot antenna backed by a rectangular cavity," IEEE Trans. Antennas Propag., Vol. 49, No. 11, 1517-1524, Nov. 2001.
11. Li, Q. and Z. Shen, "An inverted microstrip fed cavity backed slot antenna for circular polarization," IEEE Antennas and wireless Propag. Lett., Vol. 1, 190-192, 2002.
12. Hung, K. F. and Y. C. Lin, "Novel broadband circularly polarized cavity backed aperture antenna with travelling wave excitation," IEEE Trans. Antennas Propag., Vol. 58, No. 1, 35-42, Jan. 2010.
13. Pozar, D. M., Microrwave Engineering, John Wiley and Sons Inc., 2004.
14. Balanis, C. A., Antenna Theory Analysis and Design, John Wiley and Sons, Inc., 2006.
15. Saala, G., J. Hopf, and S. Lindenmeier, "Small satellite car antenna for simultaneous reception of LHCP and RHCP signals," Third European Conference on Antennas Propag., EuCap 2009, 2698-2700, Mar. 2009.
16. Saala, G., D. Muller, J. Hopf, and S. Lindenmeier, "Antenna with optimized pattern for simultaneous reception of terrestrial signals and signals of geostationary satellites," Advances in Radio Science, Vol. 8, 37-42, 2010.